Size matters: a review and new analyses of racial differences in cranial capacity and intelligence that refute Kamin and Omari

We provide a case by case examination of Kamin and Omari’s critical review (South African Journal of Psychology, 1998, 28, 119–128) concluding that race differences in head size were too small to explain their differences in IQ. Although Kamin and Omari make several valid points and identified an “anomalous” finding in two samples (that Blacks averaged greater head circumference than Whites), in the main their review is highly misleading. We find, among other things, that Kamin and Omari: (1) ignored the relation between brain size and IQ established by magnetic resonance imaging and the race differences in brain size established by MRI, autopsies, and endocranial volume; (2) erred in attributing to arithmetic errors and uncontrolled differences in sex ratio the differences in head size found from birth to age seven in the National Collaborative Perinatal Project; (3) neglected data showing that young Black girls mature faster than White girls which explains why Black girls sometimes average cranial sizes equal to or greater than their White age peers; and (4) seized upon ad hoc “alternative” findings and explanations for particular studies. When the principle of aggregation is employed and data averaged across the numerous studies, the race differences in average cranial capacity clearly emerge. New analyses in this article also confirm that whereas Blacks average proportionately longer heads, Whites and Asians average proportionately wider and higher heads, which explains why different equations for estimating cranial volume sometimes produce different results. We conclude that brain volume bears a strong relation to cognitive ability, and that increasing encephalization over evolutionary time led to progressively more spherically shaped heads with corresponding increases in head width and head height.